We propose a continuation of our initially successful study concerning the synthesis and biocidal evaluation of new organotin materials and compounds. Our initial hypothesis that mixed, "heteroleptic" organotins could exhibit a greater activity than that predicted by a simple linear variation of substituent has proven correct. Thus the mixed aryl/alkyl organotin Aryl2AIkylSnCl, arylAlkyl2SnCl, ArylAlkylSnCl2 containing various substituents will continue to be a partial focus of this research. The incorporation of sulfur, oxygen and selenium atoms within the molecular structure also offers a great opportunity for new materials and activities and will be investigated. A new series of di-tin compounds are proposed, ClR2Sn-R'-R2SnCl, R'=aryl, alkyl, where the presence of two active tin sites within the molecular structure present a special and exciting new opportunity for biological activity. We also propose a study of the organotins for the formation of antibiotic surfaces. We have preliminary evidence that mixtures of structurally dissimilar organotin chlorides create new solid state phases, hence cooperativity in this area could be important. A series of ionophore-organotins will be synthesized - they are unknown materials with a great capacity for unique biocidal activity. Together with the synthesis of the new materials, complete chemical characterization, including NMR and single crystal structural evaluation is proposed. In El Paso, we shall use an iterative process for continuous biocidal evaluation using a well-understood suite of bacteria, including the very sensitive luminescent marine bacteria that provide a rapid initial evaluation. A second investigation into the potential cooperativity of activity involves the combination of known antibiotics, e.g. nalidixic acid and organotins. There are literature hints that such cooperativity may be important. Certainly the capacity of such Lewis base antibiotics to form direct interactions with the Lewis acid organotins is clear, thus this is a promising new area of study. Since our initial biocidal screening is performed with a simple suite of bacteria we have enlarged this aspect of our study by collaborating with two research teams outside of the U.T. El Paso campus, namely Dr. Margaret Whalen, Tennessee State University, and Dr. George Eng, University of the District of Columbia. Both are specialists in various forms of biocidal activity evaluation (detailed within the proposal) in areas far from the capacity of the PI, but forming an integral portion of the iterative research activity described. Letters of agreement are attached.